/Engine/Source/Runtime/Core/Public/Tasks/Task.h
Adds the nested task to the task that is being currently executed by the current thread. A parent task is not flagged completed until all nested tasks are completed. It's similar to explicitly waiting for a sub-task at the end of its parent task, except explicit waiting blocks the worker executing the parent task until the sub-task is completed. With nested tasks, the worker won't be blocked.
namespace UE { namespace Tasks { template<typename TaskType> void UE::Tasks::AddNested ( const TaskType & Nested ) } }